1. Field of the Invention
This invention relates to nuclear event detectors and more particularly to such detectors for use in the protection of electronic equipment, especially digital electronic equipment, against the induced electrical effects of radiation, more especially gamma radiation.
2. Description of Related Art
Such a nuclear event detector is triggered into action by radiation at a flux level liable to upset or cause damage to the electronic equipment to be protected. The components of electronic equipment which particularly require to be protected are, of course, semiconductor devices. During gamma irradiation all biased semiconductor PN junctions generate a photocurrent proportional to the gamma dose rate, thus producing upset, latchup and burnout of the semiconductor devices containing such junctions. In the case of CMOS devices particularly latch up (logic elements within device being held in a fixed state) will cause the device to burnout unless the device is current limited or the power removed.
A nuclear event detector for use in protection of electronic equipment therefore includes circuit means for depowering semiconductor devices in the equipment on detection of a gamma radiation event.
In the past designers have used circuit means, utilising for example an SCR (Silicon Controlled Rectifier), single power transistors or MOSFETS, that depower the whole equipment after detecting a gamma event. However, it is often the case that not all devices require protection. Moreover, it would be desirable to arrange for some devices to retain power during and after the event to retain essential system data. By using a nuclear event detector that only locally depowers susceptible devices, the time to re-initialise the equipment e.g. computers therein, could be greatly reduced, and essential data retained in `hard` memory.